1. Field of the Invention
The present invention relates generally to underground mining and, more specifically, to a mobile belt support structure for an extendable conveyor belt used in a continuous mining operation.
2. Description of the Related Art
In the use of extensible conveyors in mining, it is usual to employ some type of collapsible belt conveyor structure in the extensible reach portion of the conveyor which may be floor mounted on individual sliding bases or carried on a stand carrier.
Mining techniques have evolved over the past several years to require larger and larger amounts of conveyor belt extensibility in mining applications, such as, for example, mining of chevron panels, as shown in FIG. 14, in which floor mounted slidable structures 1, as shown in FIGS. 15 and 16, can be conveniently used in the conveyor entry extensible reach portion 2 of an extensible conveyor system 3 for advancing or retreating motions of the angle station 4. A second extensible reach portion 5 of the system 3 is used to enter panel wing rooms with the continuous mining machine 6, to which a trailing conveyor tail unit 7 is attached. At the opposite end of the system, a belt storage magazine 8 supplies additional belting as the system is extended, while a conveyor drive 9 provides a driving force for the belt. Additionally, a trunk conveyor 10 can be used to remove material conveyed by the extensible conveyor system.
The slidable structure 1 shown in FIGS. 15 and 16 each include slidable bases 11, vertical supports 12 and troughing strand rollers 13. While these are adequate for use in the first extensible reach 2, a series of A-frame structures 14 mounted on a stand carrier 15, as shown in FIG. 17, can be more conveniently used when entering and mining the panel wing rooms which are the second extensible reach portion 5 of the conveyor. The stand carrier 15 and A-frame structures 14 are described in U.S. Pat. No. 4,860,878.
A continuous haulage system such as used in this type of mining may conveniently use two hundred feet of such slidable structure 1 in the conveyor entry portion and one thousand feet or more of such A-frame structures 14 on a stand carrier 15 in the wing portions of the panel layout. This total amount of extensibility has been uncommon previously in the mining industry.
One disadvantage of the slidable conveyor structure has been that the maximum telescopicity ratio, or ratio of extended length to collapsed length, has a practical limitation of about 20:1. Also, total frictional drag for advancing a group of such stands becomes progressively higher as more stands are used. Retreating of such stands becomes difficult when more than twenty are used in one group, since the flexibility of the connections between the stands makes the group more difficult to steer when being pushed by the tail pulley structure of the extensible conveyor.
Some of these disadvantages have been addressed by the design of the A-frame stand and stand carrier combination, in which a telescopicity ratio of up to 50:1 is possible in practical design configurations. Since the stands are carried rather than being pulled or pushed on the ground, many of the disadvantages of the slidable structure have been avoided such as to make practical the carrying of up to one thousand feet or more of collapsed conveyor structure.
The A-frame structure is not well suited to low seam applications, however, since it typically requires vertical heights of several feet to enable collapse of the structure. It is also relatively light in construction and, thereby, subject to damage if insufficient care is taken when retreating the stand carrier to collect the structure onto its carrying arms.
For these reasons, neither of the above-noted types of conveyor structure will be suitable for a new type of mining application known as "punch mining" or "highwall mining", in which a remotely operated and guided mining machine may be required to advance one thousand feet or more into a thin coal seam for example, from a highwall bench in an open pit mine or in a contour-mining situation.